Hybrid computer determines the probability distributions of instantaneous and peak amplitudes of random signals. This combined digital and analog computer system reduces the errors and delays of manual data analysis

Cameron, W. D.

English

NASA Technical Reports Server

July 1965	 Brief 65-10208 
NASA TECH 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Hybrid Computer Technique Yields Random Signal Probability Distributions 
----
1 -------- 
II RMS
]
I ________ 
Calculator
% Time A	 0 E	 bove Level
-H
_
4 IAPD 
Drift t
Compensation 
Tape And
^.ve 
Signal 
Amplification tI0h1 L	 % Time Above Level N I 
I	 Ii Il
 
9	 PAPD 
} -
[J--_-j	 No. Of Peaks Above Level N 
Analog I Digital 
Computer I Computer 
-
___L---------
___.
The problem: A complete space vehicle responds, 
during lunch, to a variety of loadings, the study of 
which requires the outputs of many sensors. Analyzing 
these data graphically by hand introduces delays and 
human error factors. A rapid, accurate determination 
of probability distributions from the sensor outputs is 
needed. 
The solution: A special digital logic computer is 
combined with a standard analog computer to deter-
mine the probability distributions of both the instan-
taneous and peak amplitudes of a random signal re-
corded on magnetic tape. 
How it's done: The instantaneous amplitude prob-
ability distribution , (IAPD) of a random signal is the 
percentage of time the signal is above some arbitrary 
value, where there are n arbitrary values to provide 
the distribution comparison. The peak amplitude 
probability distribution (PAPD) of a random signal is 
the percentage of the total number of peaks that are
above some arbitrary value where there are n arbitrary 
values. 
The recorded signal from the tape is amplified and 
fed to a low pass filter, whose output is inverted and 
subtracted from the input signal to remove the low 
frequency components identified with drift in the sens-
ing and recording devices. The RMS calculator con-
tinuously generates the root-mean-square of this infor-
mation signal. The RMS signal is rectified and routed 
to the digital logic where the two components (IAPD 
and PAPD) are determined and fed to the readout. 
To measure the percentage of time the signal is above 
some arbitrary value (IAPD), it is assumed that the 
signal exceeded that level 100% of the time, and the 
amount of time the signal was below that level is sub-
tracted. This is accomplished by dividing the logic 
time base into 10,000 equal increments and subtract-
ing one digit for each time increment the signal is 
below that level. When the time base counter reaches 
(continued overleaf) 
NW
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document. 
https://ntrs.nasa.gov/search.jsp?R=19650000206 2020-03-11T17:23:55+00:00Z
0000. it produces a carryout that stops the computer 
and feeds the answer to the readout. 
To measure the percentage of the total number of 
peaks that are above some arbitrary value (PAPD), 
comparator outputs drive one-way digital differentia-
tors. A one-way differentiator produces a blip one 
clock pulse wide when the input goes from the low 
level to the high level (goes from 0 to 1). The differen-
tiator output drives a binary upcounter. When the 
input to the counter is high, it will count up one bit at 
each clock pulse. Since the differentiator is high for 
only one clock pulse, the counter will add one bit each 
time the increasing signal crosses the set level. The 
signal, rather than the absolute value, drives the 
counter in level 0. This assures that the signal will pass 
through zero. The counter in level 0 counts only half 
the total peaks because the negative portion of the 
signal has no effect on the comparator.
Notes: 
1. Data that requires five to seven man-days to reduce 
by hand can be reduced in 30 seconds by this 
method. 
2. This method of analysis should have application in 
such nonstationary random processes as system 
characteristics in structural, electrical, atomic en-
ergy, or biomedical fields. 
3. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California, 94035 
Reference B65-10208 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to 
NASA, Code AGP, Washington, D.C., 20546. 
Source: William D. Cameron 
(ARC-34) 
Brief 65-10208	 Category No. 01


Hybrid computer technique yields random signal probability distributions

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